The present invention relates to an anchoring arrangement for a coil spring, which, in use, is to carry out transverse oscillations from a rigidly anchored end thereof, primarily for use with coil spring supported playground devices. In that connection the coil spring will be a rather heavy spring constituting the sole carrier connection between a seat and a ground support and a playing child may thus carry out resilient side rocking movements on the device.
Hereby the lower end of the spring will have to be rigidly anchored, and as expectable the spring will stand but a limited number of rocking movements, inasfar as at some time or other it will break near its rigid anchoring, where the spring is subjected to real breaking forces. With the choice of a good spring material and a suitable design of the fixed anchor means an acceptable lifetime of the spring is achievable, but yet no more than it would still be desirable to further prolong the lifetime of the spring.
The purpose of the invention is to provide an anchoring arrangement which will essentially increase the durability of the spring or ensure an unchanged durability with the use of a spring material of reduced quality and therewith of reduced price.
According to the invention the anchoring arrangement comprises fixed abutment means located adjacent a spring portion near the fixed spring end so as to effectively limit the movability of said spring portion in the axial direction of the coil spring in such a manner that this spring portion is allowed to carry out an axial movement of between 10% and 90%, preferably some 50%, of the movement length as would be incurred, without the said limitation, by an operative normal maximum bending out of the spring.
When the spring, in normal use, is reciprocally bent to and fro the spring winding portions at one side of the coil spring will approach each other equally while at the opposite side of the spring they will become increasingly mutually spaced, whereafter the situation will be inversed during the return movement of the spring. With the arrangement according to the invention, of course, the bendability of the spring will be slightly limited, when a portion of the spring cannot move entirely freely, but such a limitation is without any practical significance when it occurs only near the fixed end of the spring.
With the use of the arrangement according to the invention the spring will operate fully normally as long as its amplitude of bending oscillation is small, e.g. up to about the half of the amplitude of the normal operational maximum bending of the spring, and the said associated break influence on the spring will thus still occur just outside the fixed anchoring of the lower spring end. This weak influence, however, does not weaken the spring material in any significant manner.
What is much more important in this respect is the large amplitude oscillations of the spring and the associated heavy influence on the spring portion adjacent the fixed end of the spring. In such situations, according to the invention, the spring portion near the fixed end portion, both when moving up and down, will be stopped by hitting the said fixed abutment means, and the breaking action on the spring immediately adjacent the fixed anchoring, therefore, will not be increased, inasfar as the potential breaking effect or the surplus thereof will be transferred to the spring portion adjacent the said abutment means.
Adjacent the abutment means, however, the spring is not anchored in any fixed manner, but only supported against further axial movement, and at this place, therefore, there will be no concentrated breaking action on the spring, but the associated stress will rather be distributed over a relatively long spring portion at one and the other side of the abutment means, respectively.
This distribution or smoothening out of the breaking stress for large oscillation amplitudes accounts for the spring not constantly being break loaded just adjacent the fixed anchoring, and in practice the associated relief of this critical area has the effect that the lifetime of the spring is increased quite considerably.
In the following the invention is described in more detail with reference to the accompanying drawing.